Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/04/18

Area Forecast Discussion
National Weather Service Bismarck ND
335 PM CDT Mon Sep 3 2018 .SHORT TERM...(This evening through Tuesday) Issued at 229 PM CDT Mon Sep 3 2018 Thunderstorms are the main focus in the short term period. Overall, there are very few changes this forecast period from the previous forecast. Convection still looks to develop between 5-6 pm cdt per latest CAM model output. This is slightly later than earlier runs of the CAMS and also a little farther south. However, convection does expand quickly northward into SE Saskatchewan and SW Manitoba. Storm mode still indicates a blend with discrete supercells possible early on (especially south) with a transition to multicellular and QLCS later tonight. SPC day 1 outlook did expand the slight risk area a little farther east along the Canadian border. Latest iterations of the HRRR are supporting a possible QLCS segment pushing into the Turtle mountains late this evening. Stronger Bulk shear along the Canadian border with shear aligned almost due parallel to the convective line would support this scenario. After 06 UTC Convection appears to diminish as it moves into a more strongly capped environment over central and eastern ND, combined with the diurnal increase in CIN with the loss of heating. Continued a mention of severe this early evening west and mid to late evening central, extending as far east as a line from around Hettinger to near Bismarck and into the Turtle mountains. Areas east of this, at this time, would appear to have a limited chance of severe weather late tonight. Convection may linger through the morning over the southern James River Valley. Although we are only expecting shower activity with a slight chance of thunder. Cool high pressure builds over the area through the remainder of the day Tuesday, with temperatures in the low 60s northwest to the lower 70s in the southern James River Valley. .LONG TERM...(Tuesday night through Monday) Issued at 229 PM CDT Mon Sep 3 2018 We have introduced patchy frost into the forecast across the northwest and north central Late Tuesday night into Wednesday morning as Cool high pressure slides into northern ND by 12 UTC Wednesday. We utilized guidance on the cooler side of the envelope of solutions, but not the coolest. Later shifts can adjust as needed but we will need to monitor for possible frost/freeze highlights mainly along and north of the highway 200 corridor. Quiet weather is in store Wednesday through Thursday. A blend of model guidance produces a chance of showers and thunderstorms Thursday night into Friday morning, mainly along the International Border in an area of warm advection and weak impulsed moving through a quasi-zonal flow. Another wave moves through the region Saturday into Sunday but models are not in as good agreement here, but it does result in some slight chance pops. After the cooldown on Wednesday, Temperatures quickly rebound to values near normal through the remainder of the forecast period. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 229 PM CDT Mon Sep 3 2018 VFR conditions to begin the 18Z TAF period. Scattered to broken low vfr Ceilings this afternoon at KJMS. Otherwise clear skies elsewhere until convection begins late afternoon/early evening. Kept a VCTS at KISN as thinking now is convection may develop just east of here. Added a Tempo period at KDIK and KMOT for convection in the 03-06 UTC timeframe. With move uncertainty with convection farther east, just added a VCTS at KBIS and KJMS using latest HRRR for guidance on timing. After convection moves through winds become north to northwest and remain northerly through the rest of the 18Z TAF period. We did add a mention of MVFR ceilings developing at KJMS late tonight and lingering into Tuesday morning. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...TWH LONG TERM...TWH AVIATION...TWH
Area Forecast Discussion
National Weather Service Boise ID
908 PM MDT Mon Sep 3 2018 .DISCUSSION...Mostly clear tonight, with diminishing winds in most areas - with the exception of Baker County, where breezy northwest winds will persist a few more hours in the wake of the upper-level shortwave moving across Montana. This handled well in current forecasts, and no updates expected. && .AVIATION...VFR. Mostly clear. Surface winds light and variable. Winds aloft near 10k feet MSL west 10-20kt. && .PREV DISCUSSION... SHORT TERM...Tonight through Wednesday...Latest HRRR smoke model brings smoke from California wildfires across our southernmost areas tonight, spreading northeast over all but northernmost areas by Tesday night, and continuing Wednesday. Warming trend with Wednesday likely the warmest day of the week. Instability and moisture will provide a slight chance of thunderstorms in the Blue Mountains of western Baker County Wednesday afternoon. LONG TERM...Wednesday night through Monday...Dry southwest flow aloft will keep temperatures 5-10 degrees above normal through Friday and slightly above normal on Saturday. This pattern will continue to bring smoke at upper levels from fires in southwest Oregon and northern California. Models are trending slower on the arrival of a dry Pacific cold front, which is now expected to cross our area on Saturday. It will be followed by breezy west to northwest winds Saturday afternoon, and temperatures will lower to near normal for Sunday and Monday. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ DISCUSSION...TB AVIATION.....JS PREV SHORT TERM...LC PREV LONG TERM....JT/WH
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
646 PM CDT Mon Sep 3 2018 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION...All convection has moved well west of the three major aerodromes and should not affect them for the remainder of the evening and overnight hours. Tomorrow, after diminishing winds and a few clouds overnight, surface winds will increase to moderate levels with scattered cloudiness. Convection is expected to be too isolated on Tuesday to warrant a mention in the current TAFs. && .PREV DISCUSSION... /issued 304 PM CDT Mon Sep 3 2018/ SHORT TERM (Now through Tuesday night)...Satellite and radar images indicate convection developing across the Mexican plateau as well as along the seabreeze front moving westward across the eastern portions of the CWA this afternoon. The HRRR continues to prog convection developing across the central portions of deep south Texas the rest of the afternoon and possibly into the western portions early this evening. With the NAM and GFS progging showers and thunderstorms developing with the monsoonal moisture across northeast Mexico into southwest Texas tonight...will go ahead and mention a chance of rain across extreme western portions of the CWA tonight. Will also mention heavy rainfall with storms for this evening across the same area. Tuesday`s forecast will be challenging as the models prog some drier air across northeast Mexico into the Rio Grande valley Tues afternoon surrounded by monsoonal moisture to the west and tropical moisture across the western Gulf of Mexico. Will go with isolated showers and thunderstorms across the coastal sections of the CWA Tues morning and spread rain chances westward Tues afternoon with the seabreeze front. Expect showers and thunderstorms to increase in coverage across the offshore waters Tuesday into Tues night with the surge in tropical moisture across the western Gulf. Temperatures should be slightly not as hot as they have been the past couple of days but will continue to go warmer than MOS guidance for temperatures Tues afternoon. LONG TERM (Wednesday through Monday): Deep tropical moisture will persist across the CWA, fueling higher rain chances through the period. Forecast soundings show precipitable water values remaining near or above two inches. The combination of ample moisture, daytime heating, and weak, upper level induced troughing will support unsettled weather and higher rain chances across the CWA. Isolated to scattered showers and thunderstorms will continue locally through the rest of the period as moisture lingers under modest mid level ridging. Above normal temperatures will persist. Low temperatures will be in the 75 to 80 degree range, while afternoon high temps will range from the mid 90s near the coast to triple digits farther west. The increased cloud cover and moisture will help limit heat index values, which may periodically reach the 103 to 108 degree range, but will generally be a skosh less than that. MARINE: Tonight through Tuesday night: Seas were near 3 feet with south to southeast winds near 12 knots at buoy020 this afternoon. Moderate to strong southeast winds will develop offshore the lower Texas coast this evening with lower pressure across northern Mexico and high pressure across the western Gulf of Mexico providing an increase in the pressure gradient across the coastal waters. Will word SCEC for the offshore waters this evening as a result. The pressure gradient will weaken across the western Gulf of Mexico Tuesday with Tropical Storm Gordon moving across the eastern Gulf. Light to moderate east to southeast winds should prevail across the coastal Tuesday as a result. Not much change is expected across the coastal waters Tues night. A surge of tropical moisture is expected to move across the western Gulf of Mexico ahead of Gordon Tuesday into Tues night providing an increasing chance of showers and thunderstorms across offshore the lower Texas coast. Wednesday through Saturday night: Light to moderate southeast winds and low to moderate seas will continue. The forecast position of Gordon should be near the lower Mississippi Valley by Wednesday, with high pressure still the main player for the lower Texas coast. The wave models are not picking up on much potential swell in the long term from the influence of Gordon, forecast to move across the northeast Gulf now through Tuesday night, likely not much influence since the residence time over sections of Gulf will not be long enough to generate significantly bigger waves. Showers and tstorms will remain possible in the unsettled regime of warm waters and moist southeast flow. && .BRO WATCHES/WARNINGS/ADVISORIES...None. && $$ This product is also available on the web at: HTTP://WEATHER.GOV/RGV
Please see the 00Z aviation forecast discussion below.

AVIATION... A challenging aviation forecast is in store this period as convection chances will largely be dominated by small scale features such as outflow boundaries. Based on current radar data, it appears SAT will stand the best chance for SHRA/TSRA over the next hour or so. The next best shot at showers and storms is expected during the late evening and early morning hours, primarily from SAT/SSF westward into DRT. Should this scenario play out, we should see a decrease in convection chances from late morning into early afternoon. With daytime heating and likely plenty of outflow boundaries, another round remains possible late Tuesday afternoon and evening. PREV DISCUSSION... /ISSUED 245 PM CDT Mon Sep 3 2018/ SHORT TERM (Tonight through Tuesday Night)... The coverage of showers and storms continues to increase across the area this afternoon. The previous tropical low that was over SE Texas yesterday is now over North Texas and is helping with the abundance of activity in our northern CWA. For our western counties, broad troughing continues with high moisture values streaming in from the southwest. This same setup was in place last night and produced a couple pockets of 4+ inches of rain fall in portions of Uvalde and Bandera County. Cloud cover today has kept temperatures in check with current values in the 80s and lower 90s. For the late afternoon and evening, scattered to numerous showers and storms are expected to continue. The initial focus of a higher coverage area should be somewhere near the I35 corridor. Latest satellite imagery shows that a weak boundary is moving south across Blanco and northern Hays County. As this boundary continues to slowly slide south it should help provide as a focus for shower and thunderstorm activity. The latest runs of the HRRR and TTU WRF show this area with pockets of locally heavy rainfall through the evening hours with some weakening around the 11 pm to midnight hour. The pockets of heavier rainfall could lead to the need for a Flood Advisory or perhaps a Flash Flood Warning this afternoon and evening. The focus for possible heavy rainfall will then shift back west to areas between Del Rio and San Antonio. Model guidance is in good agreement that this is where the nocturnal low-level jet will set up. Speeds at 850 mb within the jet should be around 20-25 knots with 10 knots of southerly flow on either side of the higher winds. We can look at isentropic planes to best decipher low-level lift from the nocturnal jets and the RAP/GFS are both showing strong upglide on the 305k surface with near saturation and lapse rates around 5 C/km in this region. This should be more than sufficient for a decent area of precip to develop. The HRRR shows this occurring beginning as early as 8-9 PM with the best lift coming after midnight and continuing through the overnight hours. Not expecting a prolonged period of heavy rainfall, but pockets of heavier rain within the main precip area will be possible. Will mention locally heavy rainfall in this area too tonight. Think we are close to needing a Flash Flood Watch for tonight, especially for the western counties. Latest flash flood guidance is around 1.5 inches an hour for the areas that received locally heavy rainfall last night. PW values will be above 2 inches and these rainfall amounts will certainly be possible. However, the heaviest rainfall may occur southeast of this area where the current flash flood guidance is 3+ inches in an hour. Will hold off for now but mention the locally heavy rainfall in the grids and mention the threat for flooding in the Hazardous Weather Outlook. For tomorrow, the expected area of precip in our western counties will be diminishing after sunrise with scattered activity expected across most areas for the remainder of the day. Will show PoPs in the 30-60 percent range. Rain chances will drop off in the Tuesday Night time frame with the favored area continuing to be in the western CWA where the broad troughing continues. LONG TERM (Wednesday through Monday)... Rain chances are expected to continue to be elevated during the long-term portion of the forecast as moisture values remain high and the broad troughing/shear axis remains in place across the west. There should not be much of a surface focus to help increase coverage or amounts for much of the period. Will continue to mention locally heavy rainfall in the HWO as any additional brief downpours on already saturated soils could lead to localized flooding. There could be a potential trough axis stretching into the Central and Southern Plains by the end of next weekend. This could bring even higher rainfall chances if it were to move as far south as the ECMWF is showing. Will keep PoPs in the 20-30 percent range for now on Day 6/7. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 74 91 74 93 75 / 70 50 20 40 20 Austin Bergstrom Intl Airport 74 90 73 92 73 / 70 50 20 40 20 New Braunfels Muni Airport 74 90 73 92 73 / 70 50 30 40 20 Burnet Muni Airport 73 87 72 90 72 / 70 60 30 40 30 Del Rio Intl Airport 75 91 75 90 74 / 60 30 40 40 30 Georgetown Muni Airport 74 90 73 92 73 / 70 50 20 30 20 Hondo Muni Airport 74 92 74 93 73 / 80 50 40 40 30 San Marcos Muni Airport 74 91 73 92 73 / 70 50 30 40 20 La Grange - Fayette Regional 75 91 74 93 74 / 40 50 20 40 20 San Antonio Intl Airport 75 90 75 91 75 / 70 50 30 40 30 Stinson Muni Airport 76 92 76 93 75 / 70 50 30 40 30 && .EWX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Tuesday morning for Dimmit-Frio-Kinney- Maverick-Medina-Uvalde-Zavala. && $$ Mesoscale/Aviation...Platt Synoptic/Grids...17 Public Service/Data Collection...BMW
Area Forecast Discussion
National Weather Service North Platte NE
643 PM CDT Mon Sep 3 2018 .SYNOPSIS... Issued at 312 PM CDT Mon Sep 3 2018 H5 analysis this morning had high pressure anchored across the Mid Atlantic states with a trough of low pressure located across the swrn CONUS. An active northern stream was noted across southern Canada this morning with a tandem of short wave troughs. One over southern British Columbia and a second closed system located over southern Hudson Bay. Closer to the central and southern plains, a nice shortwave was located over southern Colorado. This feature has tracked north northeast this morning, and was located over the Palmer Divide as of mid day per WV imagery. Abundant mid level Pacific moisture, and low level Gulf of Mexico moisture, continues to stream into western and north central Nebraska today, and has led to abundant cloudiness across most of the forecast area today. The exception was over northwestern portions of the forecast area where some thin high cloudiness was noted. Readings as of 3 PM CDT ranged from 73 at O`Neill to 82 at Valentine. && .SHORT TERM...(This evening through Tuesday) Issued at 312 PM CDT Mon Sep 3 2018 Tonight and Tuesday: Fog potential and precipitation chances are the main short term forecast challenges. With respect to precipitation chances tonight: A robust upper level disturbance continues to lift across eastern Colorado this afternoon. The latest NAMNest and HRRR solns lift this activity into southwestern Nebraska, dissipating it over the central and eastern Sandhills this evening. Fairly weak deep layer shear and meager CAPE will be present across swrn Nebraska through mid evening, so not expecting much of a severe threat attm. Some adjustments were made pops especially this evening as the models have a hard time, lifting this activity into the western sandhills and nwrn Nebraska. That being said, adjusted pops downward, in the north central and west overnight as the focus for thunderstorms shifts into central and eastern Nebraska overnight. West of the main area of convection, light easterly and southeasterly winds are expected overnight. With continued favorable low level moisture advection, will insert a mention of fog in the forecast for the bulk of the CWA overnight. Will keep the mention patchy as any isolated thunderstorms overnight, would not be favorable for fog formation. Overnight lows will continue to be mild with the expected cloud cover. Readings will range from the upper 50s in the panhandle to the upper 60s in the east. On Tuesday, fog will linger into the mid morning hours before burning off. However, skies will remain cloudy to mostly cloudy across the forecast area as abundant mid and low level moisture continues to be pushed into the forecast area from the south. This will limit highs to the 70s tomorrow. Late Tuesday afternoon, a decent shortwave will lift from NE Colorado into SW Nebraska. Showers and storms will develop over NE colorado and lift into the forecast area through Tuesday evening. Confidence is fairly high for pcpn Tuesday evening as there is good model agreement between the NAM12, GFS, WARW and HREF ensembles. .LONG TERM...(Tuesday night through Monday) Issued at 312 PM CDT Mon Sep 3 2018 The threat for precipitation will carry over into Tuesday night before tapering off Wednesday morning. Surface high pressure will drop south across the Dakotas into Minnesota. This feature will force a cool front through the forecast area and focus precipitation to the south of the area over Kansas. This will bring a temporary reprieve to precipitation Wednesday into Wednesday night. The high will migrate into the northern Great Lakes Thursday into Friday. Southerly flow will commence across the area, leading to an increased chance for showers and thunderstorms across the central and eastern forecast area later in the week. A shortwave trough, followed by ridging building into the western CONUS will facilitate drier and warmer conditions for the weekend into early next week. Readings will rebound back into the lower to middle 80s with lows in the 50s and mainly dry conditions are expected. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 630 PM CDT Mon Sep 3 2018 Latest radar display shows showers and thunderstorms moving northeastward across southwest NEB south of Interstate 80. Meanwhile, latest surface obs show MVFR ceilings across much of southwest and south central NEB. Current thinking is isolated to scattered showers and thunderstorm will be a threat mainly to southwest NE south of the Sandhills through the evening hours. Thereafter spotty showers and thunderstorms will be possible across the eastern portions of the local forecast area with activity expected to be mainly outside of the area to the east. Increased chances for showers and thunderstorms then return to the area tomorrow afternoon with mention of TS at both KVTN and KLBF terminals currently. Otherwise, threat for patchy fog for much of the area late tonight into tomorrow morning. MVFR ceilings expected to affect much of southwest NEB, Sandhills and north central NEB tonight into morning. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Buttler SHORT TERM...Buttler LONG TERM...Buttler AVIATION...ET
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
931 PM CDT Mon Sep 3 2018 .UPDATE... 931 PM CDT Evening Update... Convective activity has trended substantially downward from earlier this evening. RAP mesoanalysis data depicts 1000 J/kg of MUCAPE lingers across the southern 2/3 of the forecast area at this hour, though convective outflow and diurnally induced cooling have stabilized the boundary layer with respect to surface convection. Combined outflows from earlier extensive convection have pushed the effective frontal boundary to the ILX/LOT cwa border region, though 20-25 kt southerly flow in the 925-850 mb layer exists above the stable low levels, which could continue to support some isolated shower or thunderstorm development late this evening. Some high-res guidance depict some weak/isolated shower development across parts of the region through about midnight, and have maintained some slight or low-chance category pops for this. Overall however, larger scale forcing appears to be on the decrease with short wave lifting northeast across the Upper Mississippi Valley overnight, and weak height rises depicted around the west/northwest periphery of the upper level ridge across the mid-Atlantic and Ohio Valley regions. Threat of widespread heavy rainfall appears low, though with such saturated ground from recent rounds of excessive rainfall, and the potential for additional isolated precip over the next few hours, will hang onto the flash flood watch through its midnight expiration across far northern IL. Otherwise, may see some patchy fog development overnight tonight, with extensive wet ground across the northern half of the cwa and small temp-dew point depressions. Southeast winds, while light at less than 10 mph, may keep fog from becoming too thick or extensive however. Something to monitor overnight. Ratzer && .SHORT TERM... 340 PM CDT Through Tonight... Thunderstorms continue to develop across much of northern Illinois and northwest Indiana this afternoon. Despite several hours of development today, the atmosphere remains highly unstable, supported by high dewpoint air and steep low level lapse rates. Shortwave energy still moving overhead at this time, with additional focus now along southward moving front in place across northern Illinois. So do think there will be additional development over the next several hours, and although may persist into the mid evening time frame, should see substantial diminishing coverage and intensity during that time. Despite a lowering trend of overall shear, there remains enough for some isolated organized development this afternoon. This will provide an additional threat of a few stronger storms capable of producing damaging winds. An additional continued threat will be heavy rainfall and flooding, as every storm will likely produce torrential rainfall. Rodriguez && .LONG TERM... 340 PM CDT Tuesday through Sunday... Overview...The active pattern continues through the extended with multiple chances for showers and storms. Hot and humid conditions also continue through Wednesday, but a cold front brings cooler temps to the region for the latter half of the week. Isolated afternoon storms are possible Tuesday, but I have low confidence in coverage and timing. I have higher confidence in hot and humid conditions resulting in heat indices in the mid to upper 90s. Afternoon storms should dissipate as the sun goes down. The next chance of precip arrives ahead of a cold front Wednesday morning. I have high confidence in rain across the area. Given the slow nature of the front, I think heat indices will once again be in the 90s. Luckily a cooler air mass follows the cold front with highs only in the 70s to around 80 Thursday. Guidance continues to indicate showers and some storms are possible mainly along and south of I-80 Thursday into Friday morning thanks to an upper level wave over northern IL. I have medium coverage in precip and thunder occurrence. Precip chances increase across the forecast area Saturday as an upper level wave and surface low move over the region. I have much higher confidence in precip Saturday than Sunday. Sunday may be dry, but I left low chance precip chances as some models have the low traveling a bit slower. Zonal flow aloft would suggest the active yet cooler pattern continues as waves pass over the region early next week. JEE/Rodriguez && .AVIATION... For the 00Z TAFs... 654 pm...Forecast concerns are thunderstorms early this evening...chance of fog Tuesday morning and a chance of thunderstorms Tuesday afternoon. The back edge of the thunderstorms is currently between mdw/gyy and should be weakening and slowly shifting east/northeast of the next few hours. Isolated convection may continue south of the terminals through the evening but other than a few showers...the rest of tonight currently looks quiet for the terminals. Chances for thunderstorms Tuesday afternoon look low. There may be a lake breeze that forms near the lake that could aid afternoon precip development. Tuesday will be very warm and humid with quite a bit of instability but not much of a focus for development. Opted to add prob mention with this forecast but confidence is low. Generally easterly winds early this evening are expected to turn more southeasterly later this evening and southerly overnight. Wind directions will become south/southwest by mid morning with speeds increasing into the 10-15kt range. Some gusts are possible by afternoon. Winds may turn more southerly or south/southeasterly by late afternoon/early evening. Patchy fog is possible overnight into Tuesday morning but confidence is low. Added 6sm mention at dpa/gyy but trends will need to be monitored later this evening/overnight. cms && .MARINE... 340 PM CDT A period of south winds of 15-25 kt begins Tuesday. Winds sharply turn north 10-20 kt, psbly to 25 kt behind a cold front Wednesday. A small craft advisory may be needed for hazardous waves Wednesday night into Thursday morning. Northeast winds diminish as a high builds over the western lakes Thursday. Northeast to east winds are expected through at least the first half of the weekend. JEE/Rodriguez && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Flash Flood Watch...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012 until midnight Tuesday. IN...None. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
Area Forecast Discussion
National Weather Service San Francisco Bay Area
843 PM PDT Mon Sep 3 2018 .SYNOPSIS...Look for seasonably warm conditions inland while cooler temperatures prevail at the coast in response to the marine layer. Inland areas cool by a few degrees on Wednesday when a weak trough pushes inland to our north. Inland temperatures warm back to above average across the interior late in the week as high pressure builds over the region. && of 8:43 PM PDT Monday...Onshore breezes will carry coastal stratus and patchy fog back inland tonight and Tuesday morning. Hazy and smoky conditions are still prevalent mainly aloft; the Sep 3 18z run of the HRRR modeled near surface smoke indicates hazy and smoky conditions over the Bay Area going through late Tuesday evening. A long wave trough remains located over western Canada and near the Pacific Northwest. 500 mb mean height forecasts lean toward a medium long wave ridge developing over California by early to mid next week. The upstream air flow over the Pacific Basin is chaotic and highly amplified. Recent medium range forecasts have been leaning toward a large scale block developing over the North Pacific, aside from ok agreement that the pattern will be nearly stationary they have otherwise not been settling on any particular solution or atmospheric block type, season-wise it is a bit early for blocks; the Sep 3 12z ECMWF shows short lived sharply split north-south 250 mb jet stream flow advancing eastward of Japan Mon through Wed next week. Part of the models struggle could be due to handling remnant deep tropical moisture well NW of Hawaii between 174 and 175 degrees west longitude becoming ingested into a low center W-SW of the Aleutians (and east of this low is a ridge with warm air advection fueling or building ridge heights) eventually the low incorporates more moisture from presently tropical cyclone "Jebi" according to the GFS. Growing differences in the medium range model output itself is a sign the large scale pattern is undergoing change, thus with the aforementioned description it is a primarily low confidence forecast for downstream over us late in the medium range. Climatology is the most reliable indicator out near the end of and beyond the medium range or extended period. Best guess at this point for this week and next is that we`ll continue to have more of the usual September weather late night and morning inland intrusions of coastal stratus and fog and onshore breezes strongest each afternoon and evening, ridge strength /subsidence/ determining the depth of the marine layer. Dry through the extended forecast period. && .PREV of 1:54 PM PDT Monday...Clouds have mostly mixed out over inland areas except for the typical spots along the coast and around portions of the Monterey Bay. This has allowed for modest warming in the interior where temperatures are being reported in the 80s with 60s and 70s more common near the coast and around the bays. However, with the marine layer between 1,800-2,000 feet in depth, do expect daytime highs to be slightly cooler compared to yesterday for inland areas. With the deep marine layer, look for low clouds to push back inland overnight and spread into most valley locations. This will hold overnight lows in the 50s for most urban areas once again. Not much change expected on Tuesday with temperatures near to slightly above seasonal averages across the interior. Near the coast, low clouds will linger later into the morning with cooler onshore flow. A weak short-wave trough is then forecast to push inland to our north which will help weaken the ridge aloft on Wednesday. This may also help to deepen the marine layer Tuesday night which will result in a slight cooling trend Wednesday afternoon. However, if the disturbance helps to mix out the marine layer, coastal areas may actually see more sunshine on Wednesday compared to previous days. High pressure over the Pacific will then build into southern and central California late in the week. This will result in temperatures rebounding back to above seasonal averages, especially inland while the marine layer will likely keep cooler conditions near the coast. Dry weather conditions are also likely to prevail through the forecast period. && of 4:45 PM PDT Monday...Lots of stratus along the coast. Marine layer is slightly lower today but latest models show little change in 500 mb heights through 24 hours. If this verifies stratus conditions would be similar to yesterday. But if the marine layer compresses more than expected tonight there would be less clouds in the SFO Bay Area. Will have to monitor for that. Vicinity of KSFO...VFR through the airport evening rush. MVFR cigs after 12Z. West to northwest winds 18-20 kt through 04Z. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Stratus rolling across MRY Bay this afternoon but clouds remain north and west of MRY and SNS. As usual the clouds will move over MRY and SNS a 02Z. MVFR/IFR ceilings will transition to VFR within the next hour or two, though areas of low clouds will likely hang around parts of the Monterey Peninsula through much of the day. More low clouds with likely IFR ceilings in the evening/overnight hours. && of 04:41 PM PDT Monday...Locally moderate and gusty winds will continue into the evening hours near the Golden Gate and Angel Island, as well as the outer waters north of Point Reyes. For other locations, winds are generally forecast to be less than 20 kt through the middle of the week. A light to moderate northwest swell will persist through the week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...SF Bay until 9 PM && $$ PUBLIC FORECAST: Canepa/RGass AVIATION: W Pi MARINE: Rowe Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Pittsburgh PA
757 PM EDT Mon Sep 3 2018 .SYNOPSIS... Heat, humidity and isolated afternoon thunderstorms are expected through mid-week. A late week cold front will bring better rain chance and more seasonable temperatures. Temperatures will be ten degrees cooler next weekend. && .NEAR TERM /THROUGH TUESDAY/... Evening Discussion: No major changes have been made to the forecast. Previous Forecast: Scattered showers and storms have continued to developed on the lake breeze downwind of Lake Erie and outflow boundaries. This will transition through the forecast area through the evening hours across the northwestern 1/3rd of the forecast area. Farther southwest in eastern Ohio, northern West Virginia, and southwestern Pennsylvania, enough subsidence should offset scattered storm development. HRRR wants to place isolated storms in this region, but several other of the CAMS do not. Elected to keep an optimistic dry forecast rolling, even though most would like the rainfall for their lawn. Can`t rule out a pop up storm, but if any develop they will be brief and not last long given them will quickly rain themselves out. Valley fog will develop overnight, most likely in the Allegheny river region given they will experience measurable rainfall during the day. Also the deeper gorges of West Virginia. Overnight lows will remain humid as dewpoints reside in the upper 60s to lower 70s. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Heat remains the main story for the short term with Wednesday being the hottest day of the week. Heat index values will push into the upper 90s outside of the mountains, but dewpoints will be in the 69-71F range which will be two degrees short of us reaching heat advisory criteria /100-100F threshold needed/. As the mid atlantic ridge weakens mid level heights fall allowing a weak baroclinic zone to drop south. As it moves through the forecast area during the afternoon Thursday ramped up pops to likely as their will be plenty of moisture to tap even through the trigger mechanism is fairly weak. It is possible the boundary could cross northern areas precip free since it will be moving through during the early morning hours. As this point, do not see a high water nor severe threat. Wind flow is not that strong. There should be enough movement in the storms despite PWATS around 1.7 inches that negate a flash flood threat. If I had to pick which is a greater concern at this juncture it would be flash flooding. The only location that could set a record high Tuesday and Wednesday would be Dubois as benchmarks reside at 88. All of the longer period of record sites, daily maximums sit in the low 100s. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Highlights: - Heat Wave is over - Return to Active Pattern - Temperatures just above near normal Overall good agreement amongst long range ensembles for the extended. By this weekend, there are differences where the cold front stalls/ washes out over northern West Virginia which will have affects on pop grids. The next weather system crosses Sunday. This will bring showers and storms over much of the region as the low tracks across Lake Erie. GFS is much faster getting the system through by as much as 12 hours over the ECMWF. The good news is the H5 anti-cyclone weakens allowing the westerlies to setup across the area. This spells a little relief from the hot weather as daytime highs settle back into the upper 70s to lower 80s save for the mountains. The mean off the statistical guidance is just below the high end of the temperature spread, so mid 80s are possible Friday, before a cool down this weekend. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... VFR conditions and light wind will be the general rule, as a strong ridge of high pressure remains in control. However, a thunderstorm may roll through FKL through 02Z. Also, patchy valley fog is possible late tonight, especially at FKL/DUJ, where rain has fallen today. Most fog will dissipate by 13Z, followed by scattered cumulus and another possible round of isolated to scattered convection. Outlook... The next chance for general restrictions will come Thursday with an encroaching frontal boundary. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$
Area Forecast Discussion
National Weather Service Great Falls MT
515 PM MDT Mon Sep 3 2018 .UPDATE... Quick update to reflect a quicker frontal passage than indicated in our grids, primarily using the HRRR model. && .SYNOPSIS... A cold front will advance through the region tonight, causing increasing clouds but otherwise remaining dry, except for an isolated mountain rain shower. Temperatures on Tuesday will reach the 60s and 70s, under mostly clear skies. Mainly dry, and warmer conditions are expected through the end of the work week. && .AVIATION... Updated 2315Z. A strong dry cold front continues to move south through the region and will reach KLWT just after 00z this evening. A brief period of 1 to 3 hours of gusty winds will occur behind this frontal passage, before loss of daytime heating/mixing begins to stabilize the lower atmosphere and winds begin to gradually subside. CIGS will develop and lower behind this front, especially over north-central MT, but will likely remain within the VFR range. A few mountain-obscuring showers are possible along the Rocky Mountain Front and the isolated mountain ranges to the east through 12Z/Tue. A surface high pressure quickly builds across the region overnight, resulting in light northeast to east winds continuing into Tuesday. && .PREV DISCUSSION... /ISSUED 301 PM MDT Mon Sep 3 2018/ Tonight through Wednesday...A cold front has moved across the HiLine counties west of Havre. Pressure rises behind the front are producing northwest winds around 20 kts, with gusts to around 35 kts. Expect the front to continue advancing south and east through the evening. Clouds are increasing as well, but are not expected to produce any more than an isolated mountain shower. Winds gradually decline overnight as the surface low moves away to the east, and high pressure builds over the region. Temperatures trend about 10 degrees colder on Tuesday amid this cooler airmass, with smaller changes for Southwest Montana. The westerly flow aloft transitions to weak ridging on Wednesday. This will yield continued fair weather with light winds and warmer temperatures. Wednesday night through Monday...Weak ridging moves east across the region through the end of the week. A generally west to southwest and more moist flow sets up behind the ridge bringing an isolated chance for afternoon showers through the end of the week. GFS continues to show much more shower development potential whereas the ECM keeps things mostly dry. Based on the trend this week, have leaned towards the drier solution. Another frontal system moves into the Pacific Northwest Friday, beginning to influence Montana Friday night. With good jet support expect winds to pick up out of the west Friday and Saturday, with strongest winds along the Northern Rocky Mountain Front. This system does not appear to be overly potent and breaks up over the mountains as it moves east through southern Canada. There will be a chance for isolated showers along the northern Rockies and along the Canadian border Saturday and Sunday as a result. Temperatures slowly warm to the mid 80s by Friday as a result of warm air advection in southwest flow, dropping into the low 70s to mid 60s for the weekend. Models remain in solid agreement with a continued progressive pattern until at least the start of next week. Differences emerge Tuesday into Wednesday but both GFS and ECM look to favor a slight building of high pressure over the desert southwest by the middle of the week. && .PRELIMINARY POINT TEMPS/POPS... GTF 43 64 42 77 / 0 0 0 0 CTB 38 61 38 73 / 0 0 0 0 HLN 47 69 44 81 / 0 0 0 0 BZN 43 70 43 80 / 0 0 0 0 WEY 33 72 34 75 / 0 0 0 0 DLN 42 72 41 80 / 0 0 0 0 HVR 42 64 42 77 / 0 0 0 0 LWT 41 62 40 75 / 10 0 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Tucson AZ
330 PM MST Mon Sep 3 2018 .SYNOPSIS...Scattered thunderstorms mainly from Tucson southward and eastward today. A gradual drying trend should prevail after Tuesday, with isolated thunderstorms mainly east of Tucson. Daytime temperatures will be a few degrees below average through Wednesday, then warming to near or slightly above average Thursday into this weekend. && .DISCUSSION...Satellite imagery showed mostly sunny to partly cloudy skies across much of southeast Arizona this afternoon. A few showers and thunderstorms were ongoing mainly south of Tucson to the Int`l border and across the White Mountains northeast of Safford. These storms were fairly well-behaved at the moment, and were moving toward the east at around 15 kts. Of note, the HRRR solutions have been panning out well so far this afternoon with the timing, location and movement of convection. If this trend continues, we`ll see isolated to scattered storms continuing into the early evening and we should be back in clear air mode by midnight. The upper trough which has been driving our weather will continue to do so much of this week. Showers and thunderstorms will occur again on Tuesday, though coverage and intensity should be slightly less than today. Continued westerly flow will work to push deeper moisture eastward by Wednesday, confining convection to areas mainly east and south of Tucson, and especially near the AZ/NM border. The trough finally moves out on Friday with high pressure off the southwest coast of California elongating and pushing its way into the region. This will dry things out even more on northerly flow aloft. A bit of low level moisture may still spark storms near terrain this weekend, but we`ll keep PoPs limited to the slight chance category. High temperatures through Wednesday will be 3-5 degrees below average. An increase in heights and thicknesses will then warm temperatures to near or even slightly above average Thursday into this weekend. && .AVIATION...Valid through 05/00Z. Scattered -TSRA/-SHRA through this evening, and isolated -TSRA/-SHRA Tuesday afternoon. Cloud decks from KTUS east, apart from lower thunderstorm bases, generally 8k-12k ft AGL. West of KTUS mainly FEW- SCT clouds around 10k ft AGL. SFC wind variable in direction and less that 12 kts, except brief gusts to 40 kts near stronger TSRA. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered thunderstorms into this evening with isolated showers and thunderstorms on Tuesday. A drying trend will then occur Tuesday night into the upcoming weekend, with isolated mainly afternoon and evening thunderstorms generally across Fire weather zones 152 and 153. Expect terrain driven 20-ft winds at less than 15 mph, with brief strong gusts near thunderstorms. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at